Evidence for tidal triggering of high-amplitude rapid tremor reversals and tremor streaks in northern Cascadia

We provide a new link between tectonic tremor propagation, tremor amplitude, and tidal stresses by analyzing high‐resolution tremor locations and amplitudes determined by multibeam backprojection of data from an array of subarrays. For two Cascadia episodic tremor and slip events, we observe repeati...

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Bibliographic Details
Published in:	Geophysical research letters Vol. 40; no. 16; pp. 4254 - 4259
Main Authors:	Thomas, Trevor W., Vidale, John E., Houston, Heidi, Creager, Kenneth C., Sweet, Justin R., Ghosh, Abhijit
Format:	Journal Article
Language:	English
Published:	Washington, DC Blackwell Publishing Ltd 28-08-2013 American Geophysical Union John Wiley & Sons, Inc
Subjects:	Amplitudes Cascadia subduction zone Earth sciences Earth, ocean, space Earthquakes episodic tremor and slip Exact sciences and technology Faults Marine Migration Seismic activity Seismology Shear stress Slip slow earthquake Streak Stresses tectonic tremor Tides Tremors reversals loading earthquakes faults amplitude shear stress propagation slip migration thrust tectonics Triggering high resolution
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Summary:	We provide a new link between tectonic tremor propagation, tremor amplitude, and tidal stresses by analyzing high‐resolution tremor locations and amplitudes determined by multibeam backprojection of data from an array of subarrays. For two Cascadia episodic tremor and slip events, we observe repeating, high‐amplitude rapid tremor reversals (RTRs) and tremor streaks. They tend to occur when tremor amplitudes are highest and occur almost exclusively during periods of thrust‐encouraging, tidally induced shear stress on the fault. We speculate that thrust‐encouraging shear stress from tidal loading forces trigger RTRs and streaks that energetically rerupture the weakened fault behind the slow slip front. The high rate and amplitude of tremor during RTRs and streaks stands in contrast to the hypothesis that activity at the leading edge of the slow slip zone is the most energetic and loudest. This implies that the spatiotemportal pattern of slow earthquake slip migration is even more intricate than previously reported. Key Points RTR's and streaks are high in amplitude relative to tremor at the slip front RTR's and streaks occur during slip‐encouraging tidal shear stress RTR's and streaks may be triggered by tidal loading and tidal stresses
Bibliography:	ark:/67375/WNG-4J6MRX10-D ArticleID:GRL50832 Streaks and RTRs plotted in map view. Each plot corresponds to one streak or RTR in order of occurrence from 2010 ETS (Figure ). Colored dots are tremor epicenters color coded in time (min) from blue (start time) to red (end time). Gray dots are tremor epicenters for the three days prior to each streak/RTR. Black boxes locate seismic arrays. Dashed line defines 40 km plate interface depth contour [McCrory et al., ].(a) Tidal shear stress time series computed for five locations on the plate interface bracketing the distribution of RTRs and streaks during the 2011 and 2010 ETS analysis periods. (b) Geographic locations of computed shear stress points (colored stars). Colors correspond to colors of the stress curves in Figure a. The red curve is computed at the average location of RTRs/streaks in each respective year (2011 average location shown on map as red star). Black boxes locate seismic arrays. Dashed line defines 40 km plate interface depth contour [McCrory et al., ].Supporting information istex:6A7F16BE7FA15991954EA9FDEBB1D78658BABC2A ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0094-8276 1944-8007
DOI:	10.1002/grl.50832